首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   105篇
  免费   12篇
  国内免费   51篇
测绘学   14篇
大气科学   79篇
地球物理   10篇
地质学   30篇
海洋学   14篇
综合类   21篇
  2023年   2篇
  2022年   1篇
  2021年   4篇
  2020年   5篇
  2019年   11篇
  2018年   5篇
  2017年   5篇
  2016年   5篇
  2015年   7篇
  2014年   9篇
  2013年   6篇
  2012年   9篇
  2011年   9篇
  2010年   8篇
  2009年   9篇
  2008年   12篇
  2007年   7篇
  2006年   12篇
  2005年   7篇
  2004年   9篇
  2003年   7篇
  2002年   1篇
  2001年   6篇
  2000年   2篇
  1999年   5篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1991年   2篇
排序方式: 共有168条查询结果,搜索用时 31 毫秒
11.
全球范围内的海洋生态环境恶化,不仅危及海洋经济发展,而且已影响到了人类生存环境和健康。本文根据我国近海海洋环境质量现状,探讨了生物修复技术在海洋环境污染治理中的应用,并提出了工程海藻培育技术研究的有关建议,以期为海洋环境的保护及资源的可持续开发提供新的方法和技术。  相似文献   
12.
The trends of distribution, translocation and seasonal change of heavy metal Pb were studied based on the surface and bottom water sampling in Jiaozhou Bay in 1979, and compared with those in 1990's. The results showed that the source of Pb in the bay was from wastewater and sewage in the east of Jiaozhou Bay from ocean vessels. Pb concentration was higher in spring and lower in summer and autumn, and remained stable through sedimentation in the bottom layer. The overall water quality was good in 1970's. Compared with the environmental monitoring data of 1995-1999, Pb pollution had become serious. Therefore, more efforts should be made to protect the bay from Pb pollution.  相似文献   
13.
营养盐硅和水温影响浮游植物的机制   总被引:1,自引:0,他引:1  
通过研究分析Si和水温对浮游植物生长的变化和其集群结构的改变影响,探讨了硅和水温影响浮游植物生长的变化和其集群结构的改变,本文研究发现,浮游植物生长的变化和其集群结构的改变的过程,营养盐硅和水温影响浮游植物生长变化和其集群结构改变的机制,确定了营养盐硅和水温是海洋生态系统的健康运行的动力。  相似文献   
14.
葛宁洁  柏林等 《地质论评》2001,47(2):184-187
大别造山带白马尖花岗岩体属燕山期侵入岩,为中生代大别山区岩浆活动的产物,为碰撞后花岗岩,锶,钕,同位素数据及稀土元素数据表明,白马尖花岗岩体为壳幔混合型,1.2-1.7Ga的钕模式年龄为其源岩的平均地壳存留年龄,北大别花岗岩类岩石的物质来源并不一致。  相似文献   
15.
采用了Visual C 以及Access技术,实现了模块化的公路路产管理系统,阐明了系统各模块的功能及其相互关系。  相似文献   
16.
The phytoplankton reproduction capacity (PRC), as a new concept regarding chlorophyll-a and primary production (PP) is described. PRC is different from PP, carbon assimilation number (CAN) or photosynthetic rate ( P^B ) . PRC quantifies phytoplankton growth with a special consideration of the effect of seawater temperature. Observation data in Jiaozhou Bay, Qingdao, China, collected from May 1991 to February 1994 were used to analyze the horizontal distribution and seasonal variation of the PRC in Jiaozhou Bay in order to determine the characteristics, dynamic cycles and trends of phytoplankton growth in Jiaozhou Bay; and to develop a corresponding dynamic model of seawater temperature vs. PRC. Simulation curves showed that seawater temperature has a dual function of limiting and enhancing PRC. PRC‘s periodicity and fluctuation are similar to those of the seawater temperature. Nutrient silicon in Jiaozhou Bay satisfies phytoplankton growth from June 7 to November 3. When nutrients N, P and Si satisfy the phytoplankton growth and solar irradiation is sufficient, the PRC would reflect the influence of seawater temperature on phytoplankton growth. Moreover, the result quantitatively explains the scenario of one-peak or two-peak phytoplankton reproduction in Jiaozhou Bay, and also quantitatively elucidates the internal mechanism of the one- or two-peak phytoplankton reproduction in the global marine areas.  相似文献   
17.
Vanadium occurs in multiple valence states in nature, whereas Nb is exclusively pentavalent. Both are compatible in rutile, but the relationship of V–Nb partitioning and dependence on oxygen fugacity (expressed as fO2) has not yet been systematically investigated. We acquired trace-element concentrations on rutile grains (n = 86) in nine eclogitic samples from the Dabie-Sulu orogenic belt by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) and combined them with published results in order to assess the direct and indirect effects of oxygen fugacity on the partitioning of V and Nb into rutile. A well-defined negative correlation between Nb (7–1,200 ppm) and V concentrations (50–3,200 ppm) was found, documenting a competitive relationship in the rutile crystal that does not appear to be controlled by bulk rock or mineral compositions. Based on the published relationship of RtDV and V valence with ?QFM, we suggest that the priority order of V incorporation into rutile is V4+ > V3+ > V5+. The inferred Nb–V competitive relationship in rutile from the Dabie-Sulu orogenic belt could be explained by decreasing fO2 due to dehydration reactions involving loss of oxidizing fluids during continental subduction: The increased proportion of V3+ (expressed as V3+/∑V) and attendant decrease in RtDV is suggested to lead to an increase in rutile lattice sites available for Nb5+. A similar effect may be observed under more oxidizing conditions. When V5+/∑V increases, RtDV shows a dramatic decline and Nb concentration increases considerably. This is possibly documented by rutile in highly metasomatized and oxidized MARID-type (MARID: mica–amphibole–rutile–ilmenite–diopside) mantle xenoliths from the Kaapvaal craton, which also show a negative V–Nb covariation. In addition, their Nb/Ta covaries with V concentrations: For V concentrations <1,250 ppm, Nb/Ta ranges between 35 and 45, whereas for V > 1,250 ppm, Nb/Ta is considerably lower (5–15). This relationship is mainly controlled by a change in Nb concentrations, suggesting that the indirect dependence of RtDNb on fO2, which is not mirrored in RtDTa, can exert considerable influence on rutile Nb–Ta fractionation.  相似文献   
18.
1 INTRODUCTIONSystematicstudyisusefulforhumanvisualizationandcomprehensionofanetworkofcomplicatedcompo nentsandprocessesinvolvingfrequentenergyflow ,consideringenergyasthebasisofbothstructureandprocess (Automa ,1 993) .Energylanguageisaconceptfordepictingasysteminwhichallphenomenaareac companiedbyenergytransformation .Thefunctionoftheecosystemovertheworlddependsontheenergyfixationbymarineplantphotosynthesis ,mostofthemarefixedbymicrophytoplanktonnearseasurfaceexposedtosunlight (Niebaken …  相似文献   
19.
Li  Ping  Pan  Zhenhui  Xiao  Tao  Wang  Jiading 《Acta Geotechnica》2023,18(2):921-936
Acta Geotechnica - Molding water content and compaction degree are the major factors driving differences in the microstructure, which has a control on the permeability of compacted loess. Although...  相似文献   
20.
针对河南省灾情获取效率低的现实问题,设计基于QGIS的微信小程序,实现灾情速报员属性数据空间化,并自动分配拨打电话任务,灾情调查人员及时将通过拨打电话获取的灾情信息快速上报,实时动态展布,并快速统计灾情速报信息,生成地震有感范围图和地震灾情信息汇总报告,为地震抗震救灾指挥部决策提供支持,满足河南及邻区小震、弱震较多地区地震应急、应急演练工作需求,也为其他应急系统建设提供参考。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号